Before I do a clean install - what are these?

[Let's Sekuhara!]

I had made a Yosemite boot USB drive before installing 10.10 just in case performance issues arose, and I'm glad I did because sure enough - performance became unacceptably slow after "upgrading".
So I've double backed up all my data and am now about to do a clean install of Yosemite. Not planning to restore configuration-related data such as Applications or Library data.

What I don't understand is, why are there two additional drives showing up in Disk Utility?

The drive with Macintosh HD is of course my internal drive. And then there's my Yosemite installer. I don't recognize "disk2" or "disk3". Are they partitions? If so, are they partitions of my internal hard drive or the installer drive or what?

This is not a fusion drive, just a regular HDD.
Still researching...
Thanks in advance.

 

[Intell]

The two orange volumes are disk images that contain the files that were used to create the USB drive. You can ignore them.

 

[gr8tfly]

Those are used as part of booting to the Recovery HD. They are present no matter what type of device the Recovery HD partition is located on.

 

[Let's Sekuhara!]

Thank you both for the helpful replies!
Proceeding with clean install...